Thermoplastic films are used in a wide variety of products to accomplish various functions. For example, breathable films are often employed in disposable absorbent articles (e.g., diapers, feminine hygiene products, incontinence products, etc.) that allow the passage of vapor through the diaper and into the environment while holding liquid. The film contains a filler (e.g., calcium carbonate) that causes a series of micropores to develop in the film when stretched. One shortcoming with these and other films is that they are generally formed from polyolefins (e.g., LLDPE), which are not biodegradable. Consequently, various attempts have been made to form films from a biodegradable polymer, such as an aliphatic-aromatic copolyester. Such attempts, however, were generally designed only for a specific application and lacked the wide range of flexibility in processing and physical properties often needed for films having a large number of potential uses. Further, although biodegradable, the aliphatic-aromatic copolyesters are synthetic and thus not generally renewable. Unfortunately, polymers that are both biodegradable and renewable are often difficult to melt process into a film. Gluten protein, for example, is a biodegradable, renewable plant protein that contains gliadin and glutenin protein components. When processed under temperature and shear, cysteine-rich amino acids present within these protein components can form disulfide inter- and intra-molecular bonds. Such bonds may result in the aggregation of the protein granules, which inhibits the protein from being readily melt processed into a film structure.
As such, a need currently exists for a technique for forming biodegradable, renewable films that may be readily adapted to numerous potential applications.